*In free space; in a wire and especially in coaxial cable, the
speed of signals can be much slower. Common coax cables have "velocity
factors" from 0.85 to 0.66 -- meaning that electricity (which in free
space moves at the same speed as light) travels only 85 to 66 percent as
fast through those cables.

While "a nanosecond per foot" is close enough for most applications, the
actual value is 1.01690688 nanoseconds per foot.